Spring tester



A. C. RUGE SPRING TESTER Sept. 18, 1951 Filed Dec. 14, 1944 v 3 Sheets-Sheet 1 INVENTOR Ark/16 ATTORN Sept. 18, 1951 A. c. RUGE 2,568,596

SPRING TESTER Filed Dec. 14, 1944 3 Sheets-Sheet 2 5 Z INVENTOR Sept. 18, 1951 A. c. RUGE v 8,

SPRING TESTER I Filed Dec. 14, 1944 s sheets-sheet s INVENTOR Patented Sept. 18, 1951 NT OFFICE I SPRING TESTER Arthur C. Rug'e, -"Ga'mbridge, Mass., assignor to 'Baldwirraliima' liamiltonBorporation, a corpo- --ra-tion of Pennsylvania 'ApplicationD'eceniber 14, 1944, Serial N0.568,"080

I (Chili-#161) '8 Glaims.

l 'My -invention relates generally to an -'app'arat 1 1s and'a method for testing springs as to menses- -ness and it is an objectofmy invention to provide an improved apparatus andmetho'd that areparticularlysuited for production testing where it is desired to determine *quic'kly and accurately-whether or not a given springis within specific tolerance.

In present-day :practice "it is common to specify that, between l /Mth of capacity and 'full capacity load P, the spring shall at every point come within 1 113% 'of thespecified load-deflection characteristicof K-poundsper inch-of deflection. For example, if M=4 and 12:2, then from'% "to full'capacity the spring must come within 12% of the specified stiffness at every- -poi nt.

The present customary way of verifying the tolerance is to observe or record separately the load applied and the resulting deflection, or to "construct a plot of the load-'defiectioncurve, from which the--deviation from the specified characteristic can be calculated. "This is :a slow "process and requires extremely accuratemeasurements if selection is to be held within-close limits. Supposing for instance that the accuracy of the individual measurements involved'is 1 which is verygood for-commercialdevices, then the error of observation at a given-point can be as large as The spring manufacturer is then forced to discard many springs which are in reality within tolerance, or he is liable to find that his customer rejects many springs which he-believed to "be satisfactory.

A further object-of my invention isto provide an improved apparatus controlled by a plurality 0f conditions "but adapted to be responsive only to deviations from a predetermined character- 'istic.

In my improved device and method for testing springs, the load and deflection are impressed upon respective electrical impedance-sensitive elements which are opposed electrically jins'uch 'a'manner that only the deviations'from a predetermined characteristic are indicated "or-recorded. To do this, I preferably employ bonded wire strain gages which I have demonstrated to be exceedingly precise and linear in their response to strain when properly constructed. I can also use many other impedance-responsive electrical devices, such as variable capacity'ga'ges, carbon strip gages, carbon pile gages,-electromagnetic gages, etc, "all of well-known types :and characteristics which can be readilyfoirnd in-the'literature on gagmg methods and devices. I can also employ such elementary impedanceapparent to those skilled in the art from the following description of the accompanying drawings i which Fig. '1 is a spring tolerance diagram;

Fig. 2 is a schematic outline of a testing machine embodying my invention;

Fig. 3 is a sectional plan view taken substantially on line 33 of Fig. 2;

Fig 4 is a circuit diagram for obtaining cooperative action between the factors of load-and deflection;

Fig. 5 is a modified tester employing a slide wire type of potentiometer;

1 Fig. 6 is another circuit arrangement-embodying' my invention;

'Fig. 7 is a modified load responsive means with temperature compensation;

Fig. 8 is a vertical section of a machine embodying my invention;

'9 is a diagrammatic outline of a spring testing machine employing a mechanically actu- "ated indicator operated in accordance with the principles of my invention.

In-order to-explain the principle of my invention I have-shown in Fig. 1 a typical spring tolerance diagram in which the important features mentioned above are indicated. The measurement-generally begins at load l /MxP, the corresponding deflection being di. Thedashedsection I of the curve is ordinarily not observed since it is affected by initial seating or straightening out of the spring. The straight line section 2 represents the specified K of the spring, K being defined as the ratio .P l/M P d d The shaded area 3 r'epresents the :specifie'd ltolerance within which the actual 'load defiection characteristic must lie the spring is to be accepted. It is to be recognized that this diagram-'is only one example of a tolerancespecification and is used for illustrative purposes only to make clear the functioning of my invention.

"In'Fig. 2 I show schematically one means "with which I accomplish the desired result.

projections 9 extending from head 4 by GIBIStiCE'Q/ Z.

deflection springs III.

Preferably, but not necessarily, members 1 are stiff or rigid relative to springs and III, while' springs II) are soft or limber. relative. tobothspring 5 and members 8 and 9. Members I while relatively rigid have some degree of flexibility. Each set of flexing members 1 and 8 are in "multiple, there being preferably at least three sets so.

as to provide stability to the device as shown in Fig. 3. While I have shown flexing members I and 8 in the form of cantilevers, I may use any other form of elastic member or structure so long as the load carried thereby produces a strain or deflection suited to my purpose. In testing of heavy springs I may prefer for; example to substitute members acting in direct tension or compression for flexing members I and 8. If the deflections are small I may substitute a link for spring III.

Impedance-responsive electrical elements II, I2, I3, I4 are shown here specifically as bonded wire strain gages for purposes of explanation. These elements are mounted in multiple so that they are of suflicient number and of such distribution as to satisfy my circuit and measuring requirements. I employ these elements to measure the loads or forces carried by 'members I and 8, which will be seen to be substantially proportional to the load on and the deflection of spring 5 respectively. I I I I It will further be seen that, members .1 are made sufliciently rigid so that their deflection under load is negligible relative to the deflection of spring 5, then I can, to advantage, support members 8 on the bed I 'I ofthe device instead of on block 6. In this case it is clear that the output of gages II and I2 is proportional to the true load carried by spring 5, and the output of gages I3 and I4 is proportional to the deflection of spring 5 as transmitted to members 8 by deflection springs III. In the circuit arrangement disclosed herein, I have shown how to treat the arrangement as illustrated in Fig. 2, which is more general, but it will be evident that many variations in arrangement of parts and circuits may be made without departing from the spirit of my invention.

Fig. 4 shows a circuit which is well suited to the purposes of my invention; and, while I claim this circuit specifically in combination, there are many other circuits which can be adapted, to the same end but which need not be shown since they do not constitute inventions of mine but are merely incidental to it. At the left of Fig. 4, a load bridge" comprised of responsive elements II", I2, I3 and I4 is so connected as to make the unbalanced voltage of the bridge responsive only to the load on spring 5. Elements II and I2 are connected so as to have additive.

effect in producing unbalance with load. Elements I3 and I4 are shunted with suitable resistance I8 so that forces transmitted by springs I0 do not have any net unbalancing effect upon the load bridge. Resistances I8 are easily set,

to the correct value by moving head 4 up and down with spring 5 removed; under this condi- 1 tion (of zero load on spring 5) resistances 18 are adjusted once and for all so that the load bridge remains balanced regardless of the position of head 4. Any conventional balancing device such as I9 completes the bridge.

'At theright of Fig. 4, a deflection bridge" comprised of responsive elements I3 and I4.

It will be evident that, as a result of forces carried through springs II], the unbalanceof this bridge is proportional to the deflection of spring 5. A conventional balancing device 20 completes the bridge.

A. voltage divider across the output of the loadbridge with a contactor 26 is used to obtain 2 a selectable fraction of the unbalanced voltage of this bridge which is opposed to the unbalanced .60 2c in Fig. 1; all thewhile watching indicator ,ZI of Fig. 4, which indicator has been calibrated to read in terms of the deviationof the spring. from the specified stiffness For convenience,

voltage of the deflection bridge.

'of Fig. 1.

The net unbalance between the two bridges carried to a suitable-galvanometer, or, amplifier andgindicator. or recorder 2 I, by coupling a. transformer 22- orby direct coupling, as conditions dictate. The two, bridges are powered withA. C. or D. C. voltages 23 and 24; a convenient arrangement is to 1et.23 and '24 be independent secondary windings on a transformer,the primary of which is fed by a suitable A. C. source of power. In explanation, indicator Z'I responds to the .sum of the voltage between ground and point 26 and the voltage between point 20 and the upper terminal of the deflection bridge. I If these voltages are exactly equal and opposite then it is obvious that indicator 2I will show zero reading. If these twovoltages' are not equal and opposite n di ator 2| will show a reading which results from what I call the net unbalance between the bridges. I r

s In the circuit shown, it is supposed that the output of the load bridge is greater than that of thedeflection bridge. If the reverse istrue,

the voltage divider would merely be put across the deflection bridge and a selectable fraction ,of the voltage across it opposed to that of-th'e load bridge. A more general arrangement would utilizelvoltage dividers across both bridges so that arbitrary ratios can be obtained, as will beeasilyseen. 7 II I Operatio'n.-Assume that a spring is placed in the machine for test and that an initial load is applied bringing us to point 21 in the diagram The procedure would be as follows: Set contact 26 in Fig.4 at a point on the calibrated voltage divider 25 corresponding to the specified stiffness K of thespring which is under test. Next, using either adjustment I9 or 20, or both -if desired adjustthe circuit of Fig.4 so'that the resultant unbalance shown bylindicator 2| is zero.

Now increase the load on the spring to point the indicatormighthave a portion of its scale marked good and other portions marked bad so that an unskilled operator may properly select springs without any knowledge or understanding of the mode of operation of the device. Or the indicator may be made to light a lamp or to make anaudible signal to characterizethe accept ance or rejection of. the spring.

I The above description of the operation will serve to show how simply and conveniently I accomplish mypurpose when Iwish to establish the tolerance rating of a spring. It will be seen that]; have so arranged the device that friction plays no part in the result. It will also be seen that. both tension and compression springs are readily taken care. of by simple modifications of the details of Fig. 2.

The testing of springs in torsion can be made by any simple torsion. devices in place of and 8, one possible form of torsional devices being shown in Simmons Patent No. 2,350,072 or in my copending application, Serial No. 430,921, now Patent No. 2,392,293.

Referring further to Fig. 4, it is to be noted that, whereas I have shown responsive elements in all arms of bothbridges, it is obvious that someof. these elements can. be replaced with fixed oradiustable impedance elements. not responsive to load or deflection of spring 5. Thus one element H and one element l3 would -;be suflicien-t in the load bridge and one element l3 would be sufficient in the deflection bridge. However, the arrangementI have shown is advantageous in that a higher sensitivity is obtained when more than one arm is operative and I also obtain temperature compensation by the balanced circuit arrangement shown.

Referring to Figs. 2 and 4, it may be observed thatif members 8 are attached to the bed ll of the device, so that none of their load is transmitted to members I, then my circuit would be modified as follows in order to give perfect action: (a) The elements l3 would be omitted from the load bridge; and (b) one or more elements 'II or [-2, or both, would be properly shunted and inserted in one or more arms of the deflection bridge. The result would be that the load bridge would be perfectly responsive to load on spring 5 without adjustment being required, and the deflection bridge would be so adjusted by shunting elements II and I2 that the deflection of members 1 is compensated for and its unbalanced voltage is responsive to the true deflection of spring 5.

V I have pointed out that voltage divider 25 can be calibrated to read in terms of the spring stifiness K. This is because the condition of balance of meter 2| while changing the load by P is that C'xP d where C is a constant depending upon the position of contact 26 and d is the deflection corresponding to load change P Therefore and hence the calibration may be made as stated. There are other ways of varying. the ratio of the opposing voltages which can also be made to give a calibrated scale of K. For instance, the voltages 23, and 24 impressed upon the bridges may be varied relative to each other by conventional means, in which case the two bridges, may be opposed directly without the necessity for voltage divider 26.

It may be observed that my device may be used to advantage for measuring K direct, in addition to the above-described tolerance determination. We may start at point 21 of Fig. v1 and individually balance the. load and deflection bridges of Fig. 4. say by energizing them one at a-. time and adjusting, l9 and 20, with contact 26'. set at any point but preferably somewhere near the expected value of K. Then if we increase the load to some other point 28 of Fig. l and ,rebalance meter 2|. by moving contact 25, leaving adjustments I! and 20 fixed. the final position. of contact 26 enables us to read K off on the calibrated scale. Thus, my invention serves a double purpose in the testing of springs.

In order to make the same individual device accurately perform over a wide range of spring deflections and loadings, I provide a number of interchangeable sets of deflection springs In in Fig. 2 of differing stiffnesses so that I can vary the output of the deflection bridge of Fig. 4.

It may be seen that, the stiffer the spring ID is, the greater the relative output of the deflection bridge will be for a given deflection of spring 5. In this .way I get a simple multiplying factor to apply to the. calibrated K scale by proper choice of springs ||l.- I can also achieve my purpose by, changing the degree of stiffness of elements 1 or 8 or both, as will readily be seen. Thus it may be seen thatby providing a few extra parts I can supply a device which will perform accurately over a wide range of spring characteristics. I

The modification of Fig. 5 shows an arrangement combining a strain gage or other impedance-responsive load-weighing element with a simple slide wire type of potentiometer. Corresponding parts are numbered identically to those in Fig. 2. In this arrangement I show the spring load carried by a rigid dynamometer element which may be an elastic member acting in direct stress on which are mountedstrain gages 30 and 3| responsive to the load thereon. A slide wire insulated from and carried by arm 3| projecting from block 6 is contacted by a sliding contact 32, dividing it into portions 33 and 34. Both slide wire and gages are in multiple if desired, as explained in connection with Fig. 2, in order to satisfy circuit requirements and to properly cancel out effects of eccentricity or non-uniform loading of spring 5.

Fig. 6 shows a circuit suited to the arrangement illustrated in Fig. 5. Corresponding parts" are numbered identically to those in Fig. 4. The circuit arrangement and operation are quite analogous to those of Fig. 4 and do not require detailed explanation. In Fig. 6 I have shown as means for varying the ratio of the opposed voltages rheostats 35 and 31 with contactors 36 and 38. These may be calibrated in terms of K, the spring stiffness, as explained above in the case of the system disclosed in Fig. 4. As a further variation, I have shown a simple indicator 39, which can be a galvanometer of suitable sensitivity or other indicator, recording or controlling device. Referring to both Figs. 5 and 6, it will be seen that the mechanical device and the circuit are simpler than those of Figs. 2 and 4.

Fig. 7 shows for purposes of illustration the application of electromagnetic gaging principles as a substitute for member 3|. Head 5 is supported on member 40 which is made of a magnetically sensitive elastic material such as iron, nickel, or Hypernic around which is wound a coil 4|. An identical or similar dummy member 42 with coil 43 serves as temperature compensator. Coils 4| and 43 may be in multiple and the load bridge of Fig. 6 would have coils 4| and 43 as adjacent arms. The impedance of coil 4| willbe sensitive to the load on spring 5.

In the modification shown in Fig. 8, I have provideda fluid actuated sylphon bellows Ill as the loading means for moving a specimen engaging platform II. This platform may be vertically adjusted by a screw 12 to accommodate springs of different heights. The screw and its surrounding casing 13 is suitably guided in a 7 frame H which has a head piece 15. To measurethe load actuall transmitted through a spring under test, I provide an upper platform 16 which has a plurality of radially extendin flexible arms I1, each supported at their outer ends by knife edges 18 and links 19. The arms are preferably three in number, the same as shown for the Fig. 3 arrangement. Spring 80 hold the knife edges upwardly in seating contact with the links, these springs having no other function. Strain gages are mounted on these flexible arms in the same manner as disclosed for the arms 1 of Fig. 2. To measure deflection a plurality of flexible arms 8|, preferably three, radiate out from the head structure 16 and are connected at their outer ends by springs 82 to a vertically movable rod 33. This rod is connected to the upper movable end of the sylphon bellows 10 so as to have identically the same movement as head H which will representthe deflection of the spring, except for one correction. For instance, the loading crosshead H has the combined movement of the spring deflection plus the upward movement of the upper crosshead 16 under test. Strain gages 11' and BI are secured to the flexible members 11 and 8| in the same manner as the gages are applied to flexible arms 8 of Fig. 2. The circuits previously described are then employed and their mode of operation is thesame.

In the modification shown in Fig. 9, a spring loading platen diagrammatically indicated at 50 is moved downwardly by any suitable mechanism and is adapted to compress a precalibrated standard spring of predetermined load versus ferred form in that the loading platen 5|} constitutes a'meansfor applying load to a'spring under test. Thespring 5| and lever 52 constitute means for determining variations in the test spring from a. predetermined relation between load and deflection-and the indicator 55 is conment of part may b'efm ade by those skilled in' the art without departing from the spirit of the invention as set forth in the appended claims.- Iclaim: 1. Apparatus for testing the relation between deflection of a spring and the load required to produce the deflection comprising, in combination, means for loading a spring under test, two deformable means adapted to be deformed uninterruptedly upon continuousapplication of load to the spring under test throughout its full load range, one of said deformable means being deformably responsive to deflection of the spring under test, the other of said deformable means being deformably responsive to the loadapplied to the spring under test, means operatively connecting both-of. said deformable means to the spring so as to transmit load and deflection characteristics thereof continuously to them throughout the full load range of thespring regardless of whether ornot said characteristics vary from a predeterminedrelation; and mean's controlled by both of said dejforma'blemean's-so as to provide a single coordinated indication continuously over the entire range of the spring upon variations of deflection characteristics. This spring i seated positions calibrated in term of the spring constant K which is the desired stiffness 'of the test spring. A pointer 55 secured to the lever 52 is adapted to indicate on a stationary cale 55 the movement of lever 52. In operation, fulcrum 53 will be placed in any predetermined position along lever 52 whereupon platen 50 will simultaneously compress standard spring 5| and test spring 54. If the load-deflection characteristics of sprin 54 follow a desired relation, then lever 52 will remain in a horizontal position and pointer 55 will remain at its zero position. However, any variation in the load-deflection characteristics of the test spring from a predetermined value .will cause lever 52 and pointer 55 to swing in one direction or the other from their zero position. Certain tolerance limits may be set for the springs under test, these limits being indicated by the graduation marks on scale 56. While this arrangement requires a carefully precalibrated standard spring, yet the structure is mechanically simple and its accuracy depends solely upon the care and precision with which it is made. This combination embodies certain fundamental principles in common with my prea predetermined relation between load and deflection thereof. 1 r r I 2. Apparatus for testing the relation between deflectionjof a spring and the load required to produce the deflection comprising, in combination, means for loading a spring under test, means including electrical impedance strain responsive means continuously responsive to the load throughout the full load range of the spring, means includingelectrical impedance 'stra'in responsive means continuously responsive to the deflection ofthe spring as a result of the applied load at any given instant anywhere in the full load range of the spring, electrically controlled indicatin means, and means normally continuously connected'to both of said continuously responsive impedance means and to'said indicating means so as'to actuate the latter when the relation between load and deflectionof the spring varies from a predetermined value over the entire range of the spring. 7

3. The combination set forth in claim '2 further characterizedby the provision, of means whereby the desired predetermined relation between deflection and load may be varied.

4, The combination 'set forth in claim 2 further characterized in that the load responsive means includes a yieldable member which yields which yields continuously in response to the applied load and the deflectionresponsive means also includes a yieldable member but which yields to a different extent than the load yielding element, and the indicating means is controlled in accordance with the relative yielding of both said yieldable means.

6. The combination set forth in claim 2 further characterized in that the indicating means comprises a pair of bridges, the impedance devices of the load responsive means being located in one of said bridges and the impedance device of the deflection responsive means being in the other bridge, and said bridges being balanced against each other whereby the balance is maintained so long as the respective impedance devices are varied in a desired proportion between deflection and load.

7. Apparatus for testing the relation between deflection and load of a spring comprising, in combination, means for loading a spring under test including a movable load applying element which moves in a predetermined proportion to the deflection of the spring during loadin there of, a flexible load responsive member, a flexible deflection measuring member connected by a spring to said loading means whereby movement of the latter in response to deflection of the spring under test causes the deflection measuring member to flex, electrical impedance strain gages connected to each of the flexible members, and bridges balanced against each other and respectively containing said strain gages whereby a net unbalance between the bridges occurs when the deflection and loading of a spring under test varies from a predetermined relation.

8. The combination set forth in claim 7 further characterized by the provision of means whereby the bridges may be adjusted to establish any desired relationship between the loading and deflection of a spring under test.

ARTHUR C. RUGE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 878,346 Clark Feb. 4, 1908 1,120,838 Miller Dec. 15, 1914 1,681,047 Porter 1 Aug. 14, 1928 1,874,780 McGukin Aug. 30, 1932 2,164,453 Gaskins July 4, 1939 2,170,197 Gumprich Aug. 22, 1939 2,271,739 Link Feb. 3, 1942 2,316,975 Ruge Apr. 20, 1943 2,322,319 Ruge June 22, 1943 2,356,763 Keinath Aug. 29, 1944 2,360,886 Osterberg Oct. 24, 1944 2,458,704 Hem Jan. 11, 1949 

